llvm/lib/CodeGen/AsmPrinter/DwarfStringPool.cpp

   1 //===- llvm/CodeGen/DwarfStringPool.cpp - Dwarf Debug Framework -----------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "DwarfStringPool.h"
  10 #include "llvm/ADT/SmallVector.h"
  11 #include "llvm/ADT/Twine.h"
  12 #include "llvm/CodeGen/AsmPrinter.h"
  13 #include "llvm/MC/MCAsmInfo.h"
  14 #include "llvm/MC/MCStreamer.h"
  15 #include <cassert>
  16 #include <utility>
  17
  18 using namespace llvm;
  19
  20 DwarfStringPool::DwarfStringPool(BumpPtrAllocator &A, AsmPrinter &Asm,
  21                                  StringRef Prefix)
  22     : Pool(A), Prefix(Prefix),
  23       ShouldCreateSymbols(Asm.MAI->doesDwarfUseRelocationsAcrossSections()) {}
  24
  25 StringMapEntry<DwarfStringPool::EntryTy> &
  26 DwarfStringPool::getEntryImpl(AsmPrinter &Asm, StringRef Str) {
  27   auto I = Pool.insert(std::make_pair(Str, EntryTy()));
  28   auto &Entry = I.first->second;
  29   if (I.second) {
  30     Entry.Index = EntryTy::NotIndexed;
  31     Entry.Offset = NumBytes;
  32     Entry.Symbol = ShouldCreateSymbols ? Asm.createTempSymbol(Prefix) : nullptr;
  33
  34     NumBytes += Str.size() + 1;
  35   }
  36   return *I.first;
  37 }
  38
  39 DwarfStringPool::EntryRef DwarfStringPool::getEntry(AsmPrinter &Asm,
  40                                                     StringRef Str) {
  41   auto &MapEntry = getEntryImpl(Asm, Str);
  42   return EntryRef(MapEntry);
  43 }
  44
  45 DwarfStringPool::EntryRef DwarfStringPool::getIndexedEntry(AsmPrinter &Asm,
  46                                                            StringRef Str) {
  47   auto &MapEntry = getEntryImpl(Asm, Str);
  48   if (!MapEntry.getValue().isIndexed())
  49     MapEntry.getValue().Index = NumIndexedStrings++;
  50   return EntryRef(MapEntry);
  51 }
  52
  53 void DwarfStringPool::emitStringOffsetsTableHeader(AsmPrinter &Asm,
  54                                                    MCSection *Section,
  55                                                    MCSymbol *StartSym) {
  56   if (getNumIndexedStrings() == 0)
  57     return;
  58   Asm.OutStreamer->switchSection(Section);
  59   unsigned EntrySize = Asm.getDwarfOffsetByteSize();
  60   // We are emitting the header for a contribution to the string offsets
  61   // table. The header consists of an entry with the contribution's
  62   // size (not including the size of the length field), the DWARF version and
  63   // 2 bytes of padding.
  64   Asm.emitDwarfUnitLength(getNumIndexedStrings() * EntrySize + 4,
  65                           "Length of String Offsets Set");
  66   Asm.emitInt16(Asm.getDwarfVersion());
  67   Asm.emitInt16(0);
  68   // Define the symbol that marks the start of the contribution. It is
  69   // referenced by most unit headers via DW_AT_str_offsets_base.
  70   // Split units do not use the attribute.
  71   if (StartSym)
  72     Asm.OutStreamer->emitLabel(StartSym);
  73 }
  74
  75 void DwarfStringPool::emit(AsmPrinter &Asm, MCSection *StrSection,
  76                            MCSection *OffsetSection, bool UseRelativeOffsets) {
  77   if (Pool.empty())
  78     return;
  79
  80   // Start the dwarf str section.
  81   Asm.OutStreamer->switchSection(StrSection);
  82
  83   // Get all of the string pool entries and sort them by their offset.
  84   SmallVector<const StringMapEntry<EntryTy> *, 64> Entries;
  85   Entries.reserve(Pool.size());
  86
  87   for (const auto &E : Pool)
  88     Entries.push_back(&E);
  89
  90   llvm::sort(Entries, [](const StringMapEntry<EntryTy> *A,
  91                          const StringMapEntry<EntryTy> *B) {
  92     return A->getValue().Offset < B->getValue().Offset;
  93   });
  94
  95   for (const auto &Entry : Entries) {
  96     assert(ShouldCreateSymbols == static_cast<bool>(Entry->getValue().Symbol) &&
  97            "Mismatch between setting and entry");
  98
  99     // Emit a label for reference from debug information entries.
 100     if (ShouldCreateSymbols)
 101       Asm.OutStreamer->emitLabel(Entry->getValue().Symbol);
 102
 103     // Emit the string itself with a terminating null byte.
 104     Asm.OutStreamer->AddComment("string offset=" +
 105                                 Twine(Entry->getValue().Offset));
 106     Asm.OutStreamer->emitBytes(
 107         StringRef(Entry->getKeyData(), Entry->getKeyLength() + 1));
 108   }
 109
 110   // If we've got an offset section go ahead and emit that now as well.
 111   if (OffsetSection) {
 112     // Now only take the indexed entries and put them in an array by their ID so
 113     // we can emit them in order.
 114     Entries.resize(NumIndexedStrings);
 115     for (const auto &Entry : Pool) {
 116       if (Entry.getValue().isIndexed())
 117         Entries[Entry.getValue().Index] = &Entry;
 118     }
 119
 120     Asm.OutStreamer->switchSection(OffsetSection);
 121     unsigned size = Asm.getDwarfOffsetByteSize();
 122     for (const auto &Entry : Entries)
 123       if (UseRelativeOffsets)
 124         Asm.emitDwarfStringOffset(Entry->getValue());
 125       else
 126         Asm.OutStreamer->emitIntValue(Entry->getValue().Offset, size);
 127   }
 128 }